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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
Advanced Search

To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"
  1. GRB 250424A: Enhanced Swift-XRT position
  2. GRB 250424A: AstroSat CZTI detection of a bright long burst
  3. GRB 250424A: COLIBRÍ Detection of a Bright Optical Counterpart
  4. GRB 250424A: BlackGEM optical afterglow detection
  5. GRB 250424A: VLT/X-shooter spectroscopic redshift z = 0.310
  6. GRB 250424A: likely host galaxy
  7. GRB 250424A: DDOTI Afterglow Detection
  8. GRB 250424A: REM optical/NIR afterglow detection
  9. GRB 250424A: Swift detection of a burst with an optical counterpart
  10. Swift GRB 250424A: Global MASTER-Net observations report
  11. Swift GRB 250424A: Global MASTER-Net OT detection
  12. LIGO/Virgo/KAGRA S250328ae: Subaru/PFS Spectroscopic Follow up and Candidates
  13. EP250421a: Nickel optical upper limit
  14. EP250416a / GRB 250416C: Gemini GMOS-S likely host galaxy redshift z = 0.963
  15. EP250421a: Upper limits from Fermi-GBM Observations
  16. SVOM/sb25042207: XRT observations
  17. SVOM/sb25042207: BOOTES-2 early optical upper limit
  18. SVOM/sb25042207: GOTO optical upper limits
  19. GRB 250421A: AstroSat CZTI detection
  20. SVOM/sb25042207: SVOM detection of an X-ray transient
  21. GRB250419A: VLA radio detection
  22. IceCube-250421A: DDOTI Detection of the LAST Candidate
  23. GRB 250419A: Mephisto Multi-band Optical Detection
  24. GRB 250419A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  25. IC-250421A: LAST optical observations of the IceCube neutrino candidate
  26. EP250421a: NOT optical observations
  27. GRB 250419A: Optical Observations via Virtual Telescope Project
  28. EP250421a: REM optical upper limit
  29. EP250421a: Swift/XRT counterpart detection
  30. EP250421A: COLIBRÍ Optical Upper Limit
  31. GRB 250419A: Mondy Continued Optical Observations
  32. Fermi GRB 250421A: Global MASTER-Net observations report
  33. EP250421a: Global MASTER-Net observations report
  34. GRB 250421B: AstroSat CZTI detection of a bright long burst
  35. EP250421a: Einstein Probe detection of an X-ray transient
  36. EP250421a: Mephisto optical counterpart confirmation
  37. IceCube Alert 250421.71: Global MASTER-Net observations report
  38. IceCube-250421A - IceCube observation of a high-energy neutrino candidate track-like event
  39. IceCube-Cascade 250414A: Upper limits from a search for additional neutrino events in IceCube
  40. EP250421a: JinShan likely optical counterpart
  41. The EP-WXT trigger 01709135179: Kinder optical counterpart candidate
  42. GRB 250421A: Fermi GBM Final Real-time Localization
  43. GRB 250419A: Liverpool Telescope observations
  44. GRB 250419A: LCO optical observation
  45. GRB 250419A: JinShan optical observations
  46. GRB 250419A: SVOM/VT optical continuous observations
  47. GRB 250419A: SVOM/C-GFT optical observations
  48. GRB 250419A: Swift/UVOT Follow up
  49. GRB 250416C / EP250416a: SVOM/GRM observation of a burst
  50. GRB 250419A: LCO optical afterglow multi-band observations
  51. GRB 250419A: Mondy and AbAO Optical Observations
  52. GRB 250419A: Liverpool Telescope observations
  53. GRB 250419A: AKO Optical Afterglow Detection
  54. GRB 250419A: MASTER optical afterglow observation
  55. Fermi-LAT Gamma-ray Observations of IceCube-250416A
  56. GRB 250407A: rest-frame energetics from Konus-Wind observation
  57. GRB 250419A: Swift-XRT localisation
  58. GRB 250407A: GTC/OSIRIS+ spectroscopic redshift z = 1.36
  59. GRB 250419A: VLT/X-shooter spectroscopic redshift z = 0.845
  60. GRB 250419A: Swift-XRT refined Analysis
  61. GRB 250419A: GOTO optical counterpart detection
  62. GRB 250419A: KAIT optical afterglow observations
  63. GRB 250419A: SVOM/VT optical bright counterpart confirmation
  64. GRB 250419A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  65. GRB 250419A: SVOM detection of a soft burst
  66. Konus-Wind detection of GRB 250416C (a counterpart of EP250416a)
  67. EP250416a: Swift/XRT counterpart fading
  68. EP250416a: refined EP-WXT and EP-FXT analysis
  69. Konus-Wind detection of GRB 250403A
  70. EP20250416a: Swift/XRT counterpart detection
  71. GRB 250403A: VLT/FORS2 spectroscopic redshift z = 1.847
  72. IceCube-250416A: DDOTI Optical Observations
  73. EP250416a: Gemini South-GMOS optical counterpart
  74. EP250225a: SVOM/VT optical brightening
  75. SVOM/sb25041603 is not a GRB
  76. EP250416a: GSP optical upper limit
  77. EP250416a: Global MASTER-Net observations report
  78. Fermi Gamma-ray Burst Monitor trigger 766505186/250416588 (GRB 250416A) is not a GRB
  79. EP250416a: Einstein Probe detection of an X-ray transient
  80. IceCube-250416A - IceCube observation of a high-energy neutrino candidate track-like event
  81. IceCube-250416A: Global MASTER-Net observations report
  82. Fermi Gamma-ray Burst Monitor trigger 766511207/250416657 is not a GRB
  83. GRB 250416B: Fermi GBM Final Real-time Localization
  84. GRB 250416A: Fermi GBM Final Real-time Localization
  85. SVOM/sb25041603: SVOM/COLIBRÍ (FM-GFT) Upper Limit on the Optical Counterpart
  86. SVOM/sb25041603: SVOM detection of an X-ray transient
  87. Fermi Gamma-ray Burst Monitor trigger 766474855/250416237 is not a GRB
  88. IceCube 250414.324: DDOTI Optical Observations
  89. GRB 250413A: AstroSat CZTI detection
  90. EP250304a: ATCA radio observations
  91. GRB 250412A: AstroSat CZTI detection
  92. EP250404a: Nanshan 0.43m Telescope optical observatios
  93. Fermi trigger No 766148493: Global MASTER-Net observations report
  94. Fermi trigger No 766173972: Global MASTER-Net observations report
  95. GRB 250411A: DDOTI Optical Observations
  96. Fermi GRB 250411A: Global MASTER-Net observations report
  97. GRB 250411A: Fermi GBM Final Real-time Localization
  98. GRB 250407A: Continued KAIT/Nickel optical observations
  99. GRB 250314A: e-MERLIN observations
  100. GRB 250407A: Mondy and AbAO Optical Observations

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